Redispersible polymer powders are manufactured using a spray drying process. The throughput in a spray dry tower is most dependent upon the solids content of the feed stream and the temperatures at which the process is operated. Compared with many products made by a spray drying process, redispersible polymer powders are run at very low production rates. The solids concentration in the feed stream is low due to the high viscosity associated with the polymers both dissolved and dispersed in the aqueous medium and the operating temperatures are low due to the thermal sensitivity of the product. The combination of the low solids and low temperatures yields a very low productivity for a given size dryer. The low production rates ultimately are reflected in the total manufacturing cost of producing these products.
In the manufacture of many polymer powders, the aqueous polymer emulsion is mixed with PVOH redispersant. The PVOH is dissolved in water, blended with the emulsion and the aqueous mixture is spray dried. An inert filler such as clay is blended with the spray dried powder to keep the material free flowing. When mixed with water, the PVOH within the redispersible powder dissolves and the copolymer particles are redispersed to the original wet polymer emulsion.
In some cases the amount of PVOH present in the powder product is much greater than that required to make the final product redispersible. Such higher levels of PVOH are used because of the physical properties which the PVOH imparts to the final product. These properties include improved adhesion to wood when the redispersible powder is used in a cementitious formulation such as a thin set mortar and improved blocking/storage.